This invention relates in general to an active roll control system for use in a vehicle suspension system, and is more particularly directed to an apparatus and method for improving the dynamic response of such an active roll system.
Vehicle suspension systems have as their goal the control of chassis motion during vehicle operation. One operating motion characteristic, which is controlled by known suspension systems, is chassis roll. A vehicle typically experiences chassis roll during a turning or cornering maneuver. During chassis roll, the chassis tilts or “rolls” about the vehicle's fore-to-aft axis toward an outside direction of the turn.
It is known to counteract the roll effect of the chassis by providing an opposing force to the chassis. Several methods are known to apply the opposing force. One method includes applying a chassis lifting force via corner actuators located on the vehicle side that is on the outside of the turn and/or a chassis lowering force via corner actuators located on the vehicle side that is on the inside of the turn.
Another known method is to utilize a stabilizer bar that extends laterally across the vehicle. The stabilizer bar, which is also known as a roll-control bar, acts as a torsion spring to apply the opposing force. Further, it is known to vary the opposing force that the stabilizer bar applies to the chassis. One way to vary the opposing force is to utilize and control one or more hydraulic actuators in the connection of the stabilizer bar. An example of such a system is shown in U.S. Pat. No. 5,362,094 to Jensen.
To determine the amount of roll-opposing force to be applied to the chassis, such active vehicle suspension systems require an indication of lateral acceleration to which the vehicle is subjected during the turning or cornering maneuver. In one known system, an estimated value of lateral acceleration is calculated. The lateral acceleration calculation requires a sensory input from a steerable road wheel angle sensor, a sensory input from a vehicle velocity sensor, and the value of the vehicle wheel base dimension. In one example, the road wheel angle sensor is a steering shaft angle sensor and the vehicle velocity sensor is a drive-train (e.g., transmission) sensor. Such systems can include the use of pumps and control valves directed by an electronic control unit. Such a system requires many components thereby leading to an increased cost.
Both hydraulic as well as electromechanical actuators are known. One example for a hydraulic actuator is a positioning cylinder which is actuated by hydraulic fluid. The advantage of such a system is that the actuator is of a relatively small size, while at the same time having a relatively high efficiency. That is attributable to the fact that the drive source, i.e. the hydraulic pump, may be spaced apart from the actuator. Also known are electromechanical actuators, in particular linear drives. However, these linear drives require comparatively large construction spaces in the case of high power demands, because in their case the drive source, i.e. the electromotor, cannot be spaced apart from the actuator.
Therefore, it would be advantageous to provide an electromechanical actuator, in particular a linear drive, which is characterized by a relatively small construction space while having a relatively high efficiency that provides a system to improve ride handling including a reduction in body roll which is simple and low cost.